204321 Computer Architecture

1
????????????????????????????????

• ?????????? ??????????
• ??????????????????????????
• ??????????????????????

2
???? I/O
Main Memory
Memory-mapped
I/O
Cache
I/O Controller
Processor
Display
Address Bus
Data Bus
Control Bus
Interrupts
I/O Controller
Disks
I/O Controller
Network
3
????????????????????????

• ?????????????
• Magnetic Disk
• ??????????? (????????) ?????????????????????
• ?????????????? /??????
• ????????????????????????????????
• ??????/??????? ??????
• Direct access
• Floppy, HD, ZIP, JAZ
• ???????????
• Magnetic Tape
• Sequential access
• ?????????????????????????????

• ????? ???????
• Optical Disk
• Direct access
• ??????????????????????????????????????????
• CDROM
• Compact Disk Read-Only Memory
• ????????????????? ?????????????
• CD-R
• ???????????????
• CD-R/W
• ?????????????????????????????
• ????????
• DVD
• Digital Video Disk
• ????????????

4
?????????????????????? (1)

• ????????????
• ????????? IBM ???????? Winchester (USA)
• ????????????????
• ?????????????
• ???????????????
• ?????????
• ??????????? 4 ??????? 3 ??
• ???????????????????????????????????????????
• ????????????????

• ??????????
• ????????????????????????????????
• ???????????? ???????????????????????????????
  track ????????
• ????????????????????????????????? track
  ????????????????????????
• ?????????????????????
• ????????????????????/???????????

5
?????????????????????? (2)

• ???????
• ???????????? (????)
• ????????????????? track ??????????????????????
• Movable head
• ????????????????????????
• ??????????????? track ???????????? track
• ???????????
• Contact (Floppy)
• Fixed gap
• Flying (Winchester)

• ???????????????
• ?????????????????
• ??????????????
• ????????????????????????
• ????????????????????
• ?????????????????????

6
Removable Disk

• ??????? (Floppy)
• ???? 8, 5.25, 3.5
• ?????? 1.44M (2.88M ???? ??????????)
• ???
• ?????? ????????
• ???????
• ???????

• ZIP
• ??????????????
• ???????? 100M
• JAZ
• ?????? ?????????????????
• ?????? 1-2G
• L-120 (a drive)
• ???????????????? 3.5 ???????
• ???????

7
?????????????????
Heads
arms
Track
Sector
actuator
Platters

• Disk Latency
• Queuing time Controller time Seek time
  Rotation time Transfer time
• ???????? ????????????????????????????? 4K
  (7200-rpm disk)
• Seek 8ms
• Rotation 4.2ms,
• Transfer 1ms

8
??????????????????

• ?????????? (gap) ??????? track
• ?????? ???????? ???????????????
• ????????????? track ??????????????????????????????
  ????
• ????????????????????
• ????????????? track ????????????? sector
• ?????????????????????? ???????? ????? (block)
• ?????????????????????????????? ????????
• ????????? ???????????? ???????????????????????????
  ??????????????
• ??????????????????????????????????????? OS
  ???????????????????????????????????
• ???????????????? ????????????????????

9
Time line ????????
?????????????????? ?????? (?????????)
source New York Times, 2/23/98, page C3,
Makers of disk drives crowd even more data into
even smaller spaces
10
???????????????????

• 1956 IBM Ramac early 1970s Winchester
• ????????????????????????????????????????(proprieta
  ry)
• 1970s
• 5.25 ????????
• ?????????????
• ST506, SASI, SMD, ESDI
• 1980s
• PCs workstations
• Client/server computing
• File server
• ????????????? mass product
• SCSI, IDE
• 5.25 drives ?????? PCs
• ????????? ????????? ??????????

• Late 1980s/Early 1990s
• Laptops, notebooks
• 3.5, 2.5
• ??????? DRAM, flash ??????????????? PCMCIA ?????
• ?????????????
• ????????????????????????????
• ??????? Optical disk ?????
• ????????????????????? (???)
• ?????????????????
• ??????????????????? 18 ?????
• ????????????????????
• ??????????????????? 18 ?????
• ??????????????
• ??????????????????? 18 ?????
• Seek Rotation time
• ??????????????????? 10 ??

11
RAID

• ???????????????? OS ??????????????????????
• ??????????????????????????????????????????????
  Stripping
• ??????????????? ??????? ??????????????????????????
  ?? (bandwidth, availability)
• ????????
• Redundant Array of Independent Disks
• ??????????
• RAID 0 - RAID 5 (??????????????????????????)
• Reliability
• ???????????????? N ???
• Reliability ???????? N ??? Reliability ????????
  1 ??? ? N
• 50000 ??????? ? 50 ??? 1000 ???????
• Mean-time to Failure (MTTF) ????? 6 ??????? 40 ???

12
RAID

• ????????????
• Stripping
• Mirroring/Shadowing
• Hamming Codes
• Parity
• Reed-Solomon Codes
• Failure Prediction

13
Stripping Only (RAID 0)
Physical Disk 1
Physical Disk 2
Physical Disk 3
Physical Disk 4
Logical Disk
14
StrippingMirroring (RAID 1)
Physical Disk 1
Physical Disk 2
Physical Disk 3
Physical Disk 4
Physical Disk 5
Physical Disk 6
Physical Disk 7
Physical Disk 8
Logical Disk
15
Hamming distance (RAID 2)
Physical Disk 1
Physical Disk 2
Physical Disk 3
Physical Disk 4
Physical Disk 5
Physical Disk 6
Physical Disk 7
Parity disks
Even parity p0 b0 xor b1 xor b3 p1 b1 xor b2
xor b3 P2 b0 xor b2 xor b3
Logical Disk
16
Bit-interleaved (RAID 3)
Physical Disk 1
Physical Disk 2
Physical Disk 3
Physical Disk 4
Physical Disk 5
Parity disks
1 0 0 1 0 0 1 1
1 0 1 0 0 0 1 1
0 1 1 0 1 1 1 0
1 1 0 0 1 1 0 1
1 0 0 1 0 0 1 1
Even parity p0 b0 xor b1 xor b2 xor b3
Logical Disk
17
Block parity (RAID 4)
Physical Disk 1
Physical Disk 2
Physical Disk 3
Physical Disk 4
Physical Disk 5
Parity disks
Logical Disk
18
Block distributed parity (RAID 5)
Physical Disk 1
Physical Disk 2
Physical Disk 3
Physical Disk 4
Physical Disk 5
Parity disks

• ?????????????????
• pb1?b2?b3?b4?b5
• ????????? 5 ?????
• ????????? b1 ???????
• pb1?(b2?b3?b4?b5)
• pb1?(p?b1)

• Small-write algorithm
• pb1?p?b1
• ?????????????? 2 ?????

Logical Disk
19
Problems of Disk Arrays Small Writes
RAID-5 Small Write Algorithm
1 Logical Write 2 Physical Reads 2 Physical
Writes
D0
D1
D2
D3
D0'
P
old data
new data
old parity
(1. Read)
(2. Read)
XOR


XOR
(3. Write)
(4. Write)
D0'
D1
D2
D3
P'
20
Subsystem Organization
array controller
host
single board disk controller
host adapter
manages interface to host, DMA
single board disk controller
control, buffering, parity logic
single board disk controller
physical device control
single board disk controller
striping software off-loaded from host to array
controller no applications modifications no
reduction of host performance
often piggy-backed in small format devices
21
System Availability Orthogonal RAIDs
Array Controller
String Controller
. . .
String Controller
. . .
String Controller
. . .
String Controller
. . .
String Controller
. . .
String Controller
. . .
Data Recovery Group unit of data redundancy
Redundant Support Components fans, power
supplies, controller, cables
End to End Data Integrity internal parity
protected data paths
22
System-Level Availability
host
host
Fully dual redundant
I/O Controller
I/O Controller
Array Controller
Array Controller
. . .
. . .
. . .
Goal No Single Points of Failure
. . .
. . .
. . .
with duplicated paths, higher performance can
be obtained when there are no failures
Recovery Group
23
RAID Summary

• RAID 0
• ???????????????????????
• ??????????? strip ?????????????????????????????
  round robin
• ??????????????????????/?????
• ?????????????????????????????? ???????????????????
  ???

• RAID 1
• ??????? mirror
• ??????????? strip ?????????????????????????????
  round robin
• ?????????? 2 ???????????
• ??????????????????????/?????
• ?????????????????????? ????????????????????
• ????????????????????????????????
• ????????????????
• ???????????????????????????????? copy
  ????????????????????????????????????
• ????????? down time
• ???

24
RAID Summary

• RAID 2
• ??????????? strip ??????????????? (byte/word)
• ?????????????????? (error correction)
  ?????????????????
• ???????????????? parity ?????????? hamming code
  ???????????
• ????????????????
• ??? ????????????????
• ???????????????

• RAID 3
• ???????? RAID 2
• ????????????????????????????????????????????????
  ???????????????????????????????????????
• ??? parity ???????????????
• ??????????????????????????????????????????????????
  ?
• Transfer rate ???

25
RAID Summary

• RAID 4
• ?????????????????????????????
• I/O request rate ???
• ??????????? stripped ?????????????????
• Parity ??????????????????????????? strip
  ?????????????
• ?????????????? parity disk

• RAID 5
• ????? RAID 4
• ??????????? RIAD 4 ?????????????????
• Parity ????? stripped ????????????????? parity
  ????????????? round robin
• ????????????????? server ???????????